Tomota Nishi

Independent isomer yields of Sb and Te isotopes in thermal-neutron fission of 233U, 235U and 239Pu

Independent isomer yields of 130Sb(5+, 8−), 132Sb(4+, 8−), 131Te(32+,112−) and 133Te (32+, 112−) in the thermal-neutron fission of 233U(52+), 235U(72−) and 239Pu(12+), and those of 128Sb(5+ , 8−) for 233U and 239Pu were measured by the conventional radiochemical method. The mean angular momentum −J z.xl;h of the primary fragments has been deduced from the isomer-yield ratios. The result may indicate that the value of −J tends to decrease as the number of neutrons in the Sb and Te isotopes approaches the neutron magic number, and is independent of the angular momentum of the fissioning nucleus.

Coriolis-coupling calculation of low-lying states in Ru, Pd and Cd isotopes

Abstract The theoretical potential energies and level spectra are reported for odd-mass Ru, Pd and Cd nuclei. The potential energy is calculated by taking into account the blocking effect. The level spectra are obtained by considering a collective and an intrinsic degree of freedom, where the motion of an unpaired quasiparticle in Nilssons deformed orbital is coupled by a Coriolis force with the rotational motion. For all the nuclei investigated here, the ground state spin-parity and the presence of many even-parity states and of the ccase11 2 − isomeric state are well reproduced by the model. The possible existence of shape isomeric states is suggested.

Excitation functions for deuteron-induced reactions

Abstract Excitation functions for reactions induced by deuterons on 70 Ge, 96 Zr and 130 Te were measured with the activation method up to 14.1 MeV deuteron energy. The observed reactions are 70 Ge(d, p) 71 Ge, (d, n) 71 As, (d, 2n) 70 As and (d, α) 68 Ga, and 96 Zr(d, p) 97 Zr, (d, n) 97 Nb, (d, 2n) 96 Nb and (d, 3n) 95 Nb, and further 130 Te(d, p) 131 Te, (d, n) 131 I and (d, 2n) 130 I. The results were explained with our modified Peaslee theory presented previously for 142 Ce data. Excitation functions of 96 Zr, 130 Te and 142 Ce give the common values of variable parameters and a common pattern regarding relative contributions of neutron stripping, proton stripping and entire absorption processes. The situation is quite different for 70 Ge.

Excitation functions for the reactions induced by deuterons on 142Ce up to 14.2 MeV

Abstract The excitation functions for the reactions 142Ce(d, p)143Ce, 142Ce(d, n)143Pr, 142Ce(d, 2n)142Pr and 142Ce(d, α)140La have been measured radiochemically up to a deuteron energy of 14.2 MeV. The results were well explained with a modified Peaslee theory on deuteron reactions, in which a new parameter, “entire absorption”, was introduced. The figures, which show quantitatively the contributions of the stripping and the entire absorption process for each reaction, and the contributions of the n-stripping, the p-stripping and the entire absorption process for the 142Ce+d interaction, were given. In the course of the experiment the half-life of 142Pr was determined to be 19.14±0.05 h.

Isomer-Yield Rations and Primary Angular Momenta of I, Xe and Cs Isotopes Produced in Thermal-Neutron Fission of 233U, 235U and 239Pu

The independent isomer-yields of 132 I(4 + , 8 - ), 134 I(4 + , 8 - ), 135 Xe(3/2 + , 11/2 - ) and 138 Cs(3 - , 6 - ) have been measured in the thermal-neutron induced fission of 233 U, 235 U and 239 Pu. From the isomer-yield ratios, the mean angular momenta of the primary fragements have been deduced on the basis of thc statistical analysis. Obtained results indicate that the primary angular momentum \({\langle}J{\rangle}\hbar\) is higher in odd- Z products than in even- Z ones, and increases up to a certain value at an approximate rate of \({-\varDelta}{\langle}J{\rangle}/\varDelta(\delta N){\sim}0.8\hbar\) with decreasing neutron displacements δ N , which is defined as the difference between the number of neutron N in the products and the most probable neutron number N p in the isotopic yield distribution.

The Half Life of Tb

A sample of Gd/sub 2/O/sub 3/ was borabarded for four hours with 38.5- Mev alpha particles and the activity of Dy/sup 157/ produced by the ( alpha ,3n) reaction was separated from the target material. Terbium was separated from dysprosium by an ionexchange method. The decay rate of Tb/sup 157/ nuclei was determined from the counting rate of the K x rays in a well type crystal, and the K and L electron capture ratio was measured using a NaI(Tl) crystal covered with Al, corrected for absorption by the Al cover, self absorption, photopeak efficiency, and fluorescence yield. The half life of Tb/sup 157/ was estimated at 160 ction in DDT-C/ 40 yr; a decay mode was proposed. (C.E.S.)

Mass yields of 241Am thermal-neutron fission

Mass yields of sub-threshold fission induced by thermal neutrons were investigated, namely, mass yields of 23 mass chains were determined for 241Am thermal-neutron fission by the conventional radiochemical method and by the direct γ-ray spectrometry method. The peak-to-trough ratio in terms of 99Mo/117Cd was found to be as large as 800±200. Three fission systems of spontaneous fission, sub-threshold fission and above-threshold fission with the compound mass AF = 242 were compared and discussed. The average number of neutrons released per fission was evaluated to be 4·0±0·2 from the mass yield curve.

Decay of 131Te and 133Te isomers

Abstract The absolute intensities of γ-rays of the isomers in 131 Te and 133 Te have been measured. The fractions and the internal conversion coefficients of the isomeric transitions have been determined by applying a chemical effect of the internal conversion process. Branching fractions of 133 Sb decay to 133 Te isomers were also reinvestigated.

Decay of 59.3 min 128Sn to levels of 128Sb

Abstract The γ-ray spectra associated with the decay of 59.3 min 128 Sn have been measured with Ge(Li) detectors. In order to recognize γ-rays of 128 Sn and 128m Sb, the decay and/or growth of γ-rays emitted from a tin sample separated chemically from fission products were measured. The decay of 128 Sn is followed by the intense Sb X-rays and 32.1, 45.8, 75.1, 80.9, 115.9, 152.6, 404.4, 482.3, 557.3 and 680.2 keV γ-rays. On the basis of the measured singles and γ-γ coincidence spectra and the analysis of intensities of true sum peaks, a new decay scheme has been constructed. The 10.0 min isomer in 128 Sb decays by β-emission (96.4%) to excited levels in 128 Te and by an isomeric transition (3.6 %) to the 9.1 h ground state.

The decay of 77mGe and 77As level spectrum

Abstract The radioactive decay of 77mGe (J π = 1 2; − , T 1 2 = 55.5 s ) and 77g Ge (J π = 7 2 + , T 1 2 = 11.3 h ) has been studied with the aid of Ge(Li) detectors. γ-ray spectrum measurements on the 77mGe decay and coincidence data on 77gGe decay suggest that the first excited level of 77As is at 194.5 keV. A tentative spin assignment of this level is made from the similarity of the low-energy level spectra and log ƒt values among the 75As, 77As and 79Br nuclei. A few minor changes in the previous 77gGe decay scheme are also proposed. The experimental level spectrum of 77As is compared with theoretical predictions.